1. Field of the Invention
The invention relates to a method for producing a rotary tool, and to a rotary tool produced accordingly.
2. Background Information
Hard workpieces, for example, are subjected to cutting machining using drills or milling cutters equipped with special sintered cutting inserts having a cutting-edge region which consists of a superhard material, in particular of PCD (polycrystalline diamond) or of PCBN (polycrystalline cubic boron nitride). Cutting inserts of this type are fastened integrally in a respective insert seat, which is introduced in a main tool body of the rotary tool, in particular by soldering.
A plurality of cutting inserts, for example two or three such cutting inserts, are usually fitted around the circumference of the main tool body. In a stepped tool, for example a stepped drill, further cutting inserts arranged radially further outward are fitted around the circumference in a rear region of the main tool body at a distance from a front tool point. Stepped drills of this type are used, for example, for machining a valve seat and require high-precision orientation of the cutting edges of the cutting inserts.
The main tool body consists, for example, of HSS or hard metal. The insert seats are introduced in a flute wall of a flute introduced into the main tool body and at a distance from a center longitudinal axis of the main tool body. The insert seat in this respect comprises a planar insert support and also an abutment wall arranged at the edge. The insert seat is introduced by a disk-shaped machining tool, for example a side milling cutter or a grinding wheel, such that it assumes an approximately semilunar shape.
A preformed basic cutting insert still to be machined is positioned and firmly soldered into the insert seat. The basic cutting inserts used at present in this respect have an oversize in the range of 3 to 4 mm which is still to be removed. This oversize is the result of the relatively inaccurate positioning and orientation of the prefabricated basic cutting insert in the insert seat shaped like a semilunar circle. The oversize has to be brought to a desired end contour in a subsequent finishing operation. On account of the superhard material of the cutting insert, this is associated with considerable effort. In the case of a tool in this respect, this finishing operation often requires several hours and may last up to ten hours.
The cutting inserts are usually cut out of a so-called blank by means of erosion. Alternatively, laser cutting can also be used for this purpose. The blank is a particular circular unfinished part having a layer structure with a carrier, for example made of hard metal, to which the cutting material (PCD or PCBN) is applied. As an alternative to this, the blank is formed exclusively from the cutting material.
In addition to the intended use described above, in which basic cutting inserts are firstly cut out of the blank and fastened integrally in an insert seat by soldering and then subjected to a finishing operation, such cutting inserts made of a superhard material are also used as indexable cutting inserts, which are fastened in the tool without a further finishing operation. Fine adjustment mechanisms, such as for example adjustment screws, are often provided on the tools in this respect.
A further alternative possible use for such superhard cutting inserts can be gathered from U.S. Pat. No. 5,611,251. According to such document, it is provided that firstly cutting bars with the superhard coating are formed, and these are then inserted into corresponding slots in the main tool body. In this case, the cutting bars extend over the entire tool diameter. This requires a complicated production method for the cutting inserts, however, since the cutting bars have to be equipped with the superhard cutting material on opposing sides over their length extending over the entire diameter. By contrast, simple production of the cutting inserts is made possible in the embodiment variant described above, in which the insert seats are introduced merely on one side and at a distance from the center longitudinal axis.
It is furthermore known from DE 20 2006 002 827 U1 and from EP 2067552 A1 to introduce contours into the surface of such cutting inserts, for example for forming chip breaker grooves.